The therapeutic value of progressive resistance exercises has long been recognized. Exercising muscles against progressively increasing resistance not only results in added strength and endurance in the muscles, but also in the improvement of neuromuscular coordination and in a more efficient functioning of the cardiovascular and respiratory systems.
Traditionally apparatus such as dumbbells and barbells have been used for progressive exercises. The use of such apparatus, however, can be extremely dangerous when undertaken without proper training and supervision. When a large amount of weight is being lifted, barbells are particularly dangerous and present difficult balancing problems. If they are dropped, serious injury can result to the trainee or to those about him.
In the past, various types of progressive weight training machines have been suggested to overcome the drawbacks of barbells and dumbbells. Among the most successful of these prior art devices are those that include cables and stacks of weights, such as those described in described in U.S. Pat. No. 4,093,214. In the conventional cable and weight stack system, the user selects the amount of weight to be lifted by inserting a pin in the lowermost weight of the stack to be lifted. The cable is then interconnected to the weight stack by the pin, and the lowermost weight and all weights above it are lifted when the machine is actuated.
Prior art apparatus embodying cable systems, while avoiding the drawbacks of free weights, have a drawback in that it is possible for the user to set the equipment up so that he is lifting more weight than is appropriate for that individual. This can lead to serious injury.
Thus, there presently exists a need for a safety system that permits restriction of weight selection to safe values.